Many industries require objects such as tools to be deployed through bores, such as wellbores in the oil and gas exploration and production industries, and there is always the risk of such objects becoming stuck in the bore. For example, wellbores may be drilled into the earth using long drill strings, which may become stuck, for example due to frictional engagement with the bore wall, due to collapse of the bore, due to differential pressures between the bore and surrounding formation pushing the drill string against a bore wall, due to binding with drill cuttings, or the like. Successful recovery of the drill string is of extreme importance and value to a drilling operator as the cost of failure to recover the tools and the well could run into several tens of millions of pounds.
Current methods for recovering stuck objects include impact tools known as jars which function to hammer or jar a stuck object. Drilling jars are universally employed globally by companies in the drilling and construction of oil and gas wells. However, current jarring technology has not changed or evolved for several decades, and is extremely limited in its functionality. For example, existing jarring tools may be considered to be slow, imprecise, hazardous, costly and damagingly large scale and slow rate.
Generally, a drilling jar is a mechanical device used downhole to deliver an impact load to another downhole component such as a bottom hole assembly (BHA). Known drilling jars operate by storing energy in a drilling string, for example by applying tension within the string, and suddenly releasing this energy to cause two impact surfaces to move axially and strike each other, creating an impact or jarring force within the drill string. This conventional drilling jar technology is known as a ‘Linear Jarring’ method and offers limited functionality and presents several significant drawbacks during its operation, such as:                Each impact has a high recoil force which reverberates back to the rig, shaking and impacting the rig derrick and superstructure detrimentally.        Time between impacts is lengthy—up to 2 minutes between impacts.        The inability to readily adjust the magnitude of a generated jarring force, as this is conventionally set at a predetermined value prior to the drilling jar being deployed.        Re-setting of the jar between impacts requires a force to be applied to the jar and drill-string in the opposite direction, consequently pushing the stuck drill-string back into the problem portion of the well.        High amplitude/low frequency jarring (large impact force with long intervals between impacts, which is a feature of linear jarring) is often the cause of further hole collapse and can add to the problem which is trying to be resolved.        High amplitude/low frequency impact performs poorly in freeing stuck pipe in clays and shales, which are a common rock type to cause sticking of pipe and hole instability.        High amplitude/low frequency jarring performs poorly in addressing stick-slip binding of a drill string, in which a single jar only achieves a small slipping motion before the drill string sticks again.        
Various drilling jarring tools and methods are disclosed in, for example, U.S. Pat. No. 7,882,906, U.S. Pat. No. 3,199,933, U.S. Pat. No. 1,653,093, U.S. Pat. No. 1,653,094, U.S. Pat. No. 1,901,513, U.S. Pat. No. 2,146,454, U.S. Pat. No. 2,153,883, U.S. Pat. No. 3,139,933, U.S. Pat. No. 4,890,682, U.S. Pat. No. 7,191,852, U.S. Pat. No. 4,576,229, WO 2009/134886 and U.S. Pat. No. 6,845,818.